News / Species Spotlight / Revisited: Coralline Algae (12/02/15)

Revisited: Coralline Algae

by Charles J. Hanley III

Scientific Name: Numerous
Common Name(s): Coralline Algae


Domain: Eukarya
Kingdom: Protista
Phylum: Rhodophyta
Class: Rhodophyceae
Order: Corallinales
Family: Corallinaceae
Genera: Numerous


In a little bit of a departure from the normal Species Spotlight subject matter, this installment of our popular series focuses on an often overlooked inhabitant of marine aquaria, Coralline Algae. These beautiful organisms add color, structure, and other benefits to marine systems. In marine husbandry, good coralline growth is indicative of the overall health of an aquarium, and most aquarists strive to achieve it. In addition to its aquarium benefits, the algae also play important ecological roles, including cementing coral reefs together. Its tough, its purple (most of the time), and it has a lot to offer, so lets take a closer look at coralline algae.

Corallines, not surprisingly, are red algae (phylum Rhodophyta). Though green (phylum Chlorophyta) and golden-brown (phylum Heterokontophyta) algae are more recognizable, red algae is actually the most numerous, in terms of marine species. Only a handful exists outside of the marine environment, inhabiting freshwater or soil. Rhodophyta algae owe their red/purple color to a group of pigments called phycobilins, which also act to mask the green of their chlorophylls. These unique photosynthetic pigments of red algae, allow them to be the deepest lived group, with some species surviving in waters nearly 900 ft deep. At the same time, there are species existing in the shallowest possible depths, including being tidally exposed. In other cases, some Rhodophyta species have lost their chlorophyll altogether, and live solely as parasites on other types of algae.

Coralline algae are special because they secrete calcium carbonate inside their cell walls. The calcified skeleton (called a thallus), allows corallines to grow in many places other algal species cannot, such as intertidal zones, reef crests, and areas of heavy surf. Coralline algae come in two basic types: geniculate (articulated) and nongeniculate. The phrasing refers to the presence or absence, respectively, of uncalcified joints called genicula. Geniculate corallines, like those of the genus Corallina, are branched and able to flex at the genicular joint. As such, they are capable of withstanding the heavy mechanical disturbances associated with life in the ocean, where waves and currents are predominant factors. They typically attach to hard substrates, or live as epiphytes on other organisms. The other types of coralline algae are nongeniculate, though sometimes they are imprecisely referred to as crustose. Crustose corallines are nongeniculate, but there also exist nongeniculates which are not crustose.

In the aquarium industry we most often encounter encrusting and plate-like forms of nongeniculate coralline algae, most of which are encrusting. They usually come in shades of pink, red, and purple, and hues can range from pale to intense. Some corallines may also have elements of blue, but purple and maroon are by far the most commonly seen. The surface of aquarium corallines can be smooth or rough, and the presence of reproductive structures called conceptacles is sometimes obvious.

Natural Habitat and Ecology:

There is a great word which describes many types of marine organisms. It is ubiquitous, and it means everywhere, omnipresent, universal, widespread, and worldwide. Coralline algae are truly ubiquitous throughout the entire oceanic photic zone, with some species being able to photosynthesize down to 600 ft. At that depth, light intensity is but a fraction of that at the surface. Other species live in extreme shallows, where severe light levels, powerful wave action, and prolonged low-tide exposure present constant dangers. Coralline algae are found in warm equatorial waters, frigid polar seas, and every latitude in-between.

Though coralline algae are important components of shallow seas all over the world, they are especially significant in tropical environments. In particular, encrusting corallines are critically important in coral reef ecology. They are noteworthy reef-building organisms because of their ability to deposit calcium carbonate in their thalli. The other role they play is even more crucial, since they act to cement the entire reef together. The coral rubble that creates the bulk of the reefs structure is actually secured in place by corallines. The algal skeletons are far stronger than those of scleractinians, as evinced by the overwhelming presence of corallines on reef crests. In point-of-fact, reef crests are often called algal ridges because corallines are one of the few organisms able withstand the rugged conditions presented by such shallow water. Hawaiian reefs typify this structural regime, where Porolithon sp. algae are so predominant that the crest is usually called the Porolithon ridge.

The other significant benefit coralline algae confer is that they often inhibit the growth of other types of algae. They also resist predation by herbivorous grazers, further ensuring that they are the dominant algal form on coral reefs.

Aquarium Care:

When one discusses the care of aquarium organisms, it is usually helpful to try and identify them as accurately as possible. Unfortunately, identifying captive species of corallines is difficult at best, as algae are typically classified according to specific characteristics of their reproductive cycles. In rare instances, it may be possible to use the conceptacles as a means of identification, though there is certainly no guarantee of this. Fortunately, there is little to no benefit from being able to differentiate between the species you might encounter, because the coralline algae in tanks are almost always hitchhikers on live rock collected from the wild. Since those hitchhikers were hardy enough to make it there in the first place, and since water quality needs are essentially the same for all tropical species, it matters little which particular ones are present.

Water parameter requirements for coralline algae and Small-Polyped Scleractinian (SPS) corals are principally the same. Clean water with good flow is crucial, as is pH stability. The water should be oxygen-rich and alkalinity levels must be maintained between 7.0 and 10.0 dKH. Additionally, coralline algae require plenty of calcium, strontium, and Iodine to produce new growth. In fact, coralline algae demand a significant amount of calcium, and will contribute to its depletion in a closed system. Therefore, calcium supplementation is a must to induce extensive coralline growth.

Of all factors, lighting is probably the most critical for controlling the composition and location of coralline algae colonies within aquarium systems. Illumination requirements, as previously alluded to, vary greatly from one species to another. Coralline algae that have found their way into tanks are likely to need at least moderately lit conditions, since most live rock is collected in relatively shallow water. That being said, aquarists have little control over what type of coralline they get, and few care to tailor their lights toward the algae. Most often, aquarium corallines prefer less light as opposed to more, which is why colonization first tends to occur along the bottoms and sides of the tank. Eventually, growth occurs in the upper levels of the tank as well, as differing species begin to assert themselves in their preferred regions.

Coralline growth benefits marine aquaria by helping to prevent the development of other types of nuisance algae. Additionally, some cnidarians polyps may be better able to adhere to coralline algae than bare rock, glass, or acrylic. In some ways, however, the greatest contribution coralline algae can make is to be an indicator for the overall health of an aquarium system. Corallines exhibiting rapid expansion, good coloration, and little to no white (read dead) spots are indicative of a thriving marine system. As if the aforementioned reasons were not enough, the algae are also beautiful, being far more attractive than bare rock.

To further facilitate the rapid spread of coralline algae, there are a couple of simple techniques that can be implemented. First, establishing SPS-friendly water parameters from day one is helpful. If the previously mentioned micronutrients are kept at adequate levels during the initial cycling phase, coralline algae can begin to be evident by six weeks into a new tanks life. Second, a well-colonized piece of live rock placed directly in front a powerhead helps algal spores distribute more easily throughout the rest of the tank. Because red algae spores are not motile like those of other kinds, a powerhead significantly speeds up the colonization process. Third, an aquarist can remove pieces of living coralline algae from a healthy colony, crush them up, and spread them around to bare areas.

In achieving good coralline growth, an aquarist knows that they have maintained exceptional water quality with a good balance of micronutrients. Couple that with the lovely purple backdrop that offsets coral coloration, and it is easy to see that coralline colonies are well-worth cultivation.

Quick Notes:

  • Coralline algae is ubiquitous in the worlds oceans, and lives in depths from zero to 600 feet.
  • Their calcium carbonate thalli are extremely strong, and actually cements coral reefs together.
  • Aquarium corallines typically prefer low to moderate lighting, and SPS-friendly water conditions.
  • Rapid coralline expansion can be enhanced by strong water flow directed across well-established colonies.

Works Cited:

Brightwell, C.R.Marine Chemistry. T.F.H Publications: Neptune City. 2007.

Cole, K.M., R.G. Sheath (editors). Biology of the Red Algae. Cambridge University Press: Melbourne. 1990.

Ehrenreich I. Articulated Corallines. Monterey Bay Aquarium Research Institute. 2001. URL: <>

Huber, Peter Castro and Michael E. Marine Biology 5th Ed. Boston: McGraw Hill. 2005.

Roth, M. Nongeniculate Corallines. Monterey Bay Aquarium Research Institute. 2001. URL: <>

Thurman, Harold V. and Alan P. Trujillo. Introductory Oceanography, Tenth Edition. Upper Saddle River; Pearson Prentice Hall. 2004.

Tullock, John H. Natural Reef Aquariums; Simplified Approaches to Creating Living Saltwater Microcosms. T.F.H Publications: Neptune City. 2001.